Frequency of TT-specific IgG ASCs and rTT.C-specific PBMCs. At day 0 or days 6 to 7 after immunization with TT, the frequency of TT-specific IgG ASCs (▦), rTT.C-specific IgG ASCs (▪), or rTT.C-specific CD19⁺/CD27^high PBMCs (▨) in the peripheral blood of 11 and 9 healthy donors, respectively, showed comparable results in ELISPOT and flow cytometry. The mean frequencies and SD are given.